Subnetting, Network Masks, and CIDR

In computer networking, subnetting is the practice of dividing a single network into multiple smaller sub-networks. This is done to improve network performance and security by controlling the flow of data between different parts of the network. Subnetting is accomplished through the use of network masks and CIDR (Classless Inter-Domain Routing).

A network mask is a 32-bit binary number that is used to identify the network portion and the host portion of an IP address. The network portion of an IP address is the portion that identifies the network to which the device belongs, while the host portion is the portion that identifies the specific device on that network. By using a network mask, we can divide an IP address into the network portion and the host portion.

For example, consider the IP address 192.168.1.100 with a network mask of 255.255.255.0. This network mask indicates that the first 24 bits (or 3 octets) of the IP address identify the network portion, while the last 8 bits (or 1 octet) identify the host portion. In this case, the network portion of the IP address is 192.168.1, and the host portion is 100.

CIDR is a more recent method of subnetting that allows for greater flexibility in network design. CIDR uses a slash notation to indicate the network mask. For example, the network mask 255.255.255.0 can be represented as /24 in CIDR notation. The number after the slash indicates the number of bits in the network portion of the IP address. In this case, there are 24 bits in the network portion and 8 bits in the host portion.

CIDR notation allows for more precise control over the size of sub-networks. For example, a network with a network mask of 255.255.255.0 can be subnetted into four smaller networks, each with a network mask of 255.255.255.192 (/26 in CIDR notation). This would allow for up to 64 devices on each sub-network, instead of the maximum of 254 devices allowed on the original network.

Subnetting also improves network security by limiting the broadcast traffic on each sub-network. Broadcast traffic is traffic that is sent to all devices on a network, regardless of whether they are the intended recipient. By limiting the number of devices on each sub-network, the amount of broadcast traffic is reduced, which improves network performance and security.

In summary, subnetting is the practice of dividing a single network into multiple smaller sub-networks. This is accomplished through the use of network masks and CIDR notation. Network masks are 32-bit binary numbers that are used to identify the network and host portions of an IP address, while CIDR notation allows for more precise control over the size of sub-networks. Subnetting improves network performance and security by controlling the flow of data between different parts of the network and reducing the amount of broadcast traffic.